The lip seal fitting of the present invention is of the same general type described in U.S. Pat. No. 3,672,704 which issued June 27, 1972 in the name of the present inventor.
The invention described in U.S. Pat. No. 3,672,704 involves a pair of end fittings. One fitting terminates at a seal in the form of a concave annular disc comprising a blend of several arcs. One of the arcs forms a heel constituting an annular bearing surface. Another of the arcs forms a cantilevered spring or deflecting beam having a toe constituting an annular sealing surface. The annular sealing surface is held tightly under a spring tension caused by a compression of the deflecting beam as the fitting is tightened.
Since the seal of the fitting described in U.S. Pat. No. 3,672,704 depends to a large extent upon spring tension concentrating forces at relatively narrow sealing surfaces, instead of upon a broad face-to-face metal deformation, less torque is required to make a metal-to-metal gas-tight seal with the fitting of U.S. Pat. No. 3,672,704 as compared with the prior art existing at that time.
Also, the fitting described in U.S. Pat. No. 3,672,704 enables the beam to be loosened and re-sealed many times without causing permanent deformation which often occurs in fittings of the prior art at that time. Another feature of the fitting described in U.S. Pat. No. 3,672,704 as compared with the prior art fittings, is that any increase in gas pressure inside the fitting additively acts upon the spring tension to increase the seal at the toe of the deflecting beam.
The fitting assembly of the present invention is constructed to incorporate the features and advantages of the fitting described in U.S. Pat. No. 3,672,704, but to be of a configuration which is simpler to construct, and one which is not susceptible to stress failure, for example, at the hinge point of the deflecting beam.
The assembly of the invention is constructed so that the face of the fitting, including the face of the annular sealing disc or beam, is concave and of a single predetermined radius, so as to have a single arc from the outer perimeter of the fitting to the inner perimeter or toe of the annular deflecting beam, with the outer and inner perimeters of the arc forming the seal points.
The configuration of the face of the fitting of the invention assures that it will bottom out at the outer perimeter, rather than at some intermediate point, as is the case of the fitting of U.S. Pat. No. 3,672,704. This assures minimum installation torque requirements for the fitting of the invention because the pressure point of the beam is always concentrated at the inner perimeter or toe of the deflecting beam.
Moreover, the fitting of the invention is constructed to minimize stress concentration at the hinge line between the deflecting beam and the remaining portion of the fitting by maximizing the single arc radius on the face of the fitting. This reduces the likelihood of fatigue cracks occurring at the hinge line as compared with the prior art assemblies.
Another feature of the fitting of the invention is that it is simpler and less expensive to make than the prior art fittings. This is because the face of the fitting is shaped as a single arc as compared with the blend of arcs described, for example, in U.S. Pat. No. 3,672,704.